Publications

Oligocene lacustrine deposits of the Pematang Brownshale Formation, are proven source rocks in Central Sumatera Basin, and correlate with several hydrocarbon fields such as the Kurau and Melibur fields in the east side of the basin. . The sediments are syn-rift deposits that record the initial opening of the Central Sumatera Basin. Several wells have penetrated the Pematang Brownshale Formation in the central and eastern parts of the basin. As such, in these areas, the formation has been studied in relative detail. In contrast, in the western part of the basin, the understanding of this formation is very limited. Along the western margin of the basin, the formation has been uplifted as a consequence of the Bukit Barisan orogeny. S-1 well, located in the western part of the Central Sumatera Basin, encountered 2,000 ft of the Pematang Brownshale Formation, comprising thick non-calcareous grey shale with sandstone, siltstone, and rare coal. Biostratigraphic data reveal the formation was deposited in a supralittoral environment during the Oligocene to earliest Miocene. An isochrone map of top Pematang Brownshale Formation to Basement was integrated with biostratigraphy data, wireline log, and seismic to generate a paleogeography map of the western part of the Central Sumatra Basin. The paleogeography map shows that the sediment was deposited in a closed lacustrine setting. Sediment supply is thought to have originated from the northeastern area (Ujungpadang nose), in contrast with previous research by Cameron (1983) who suggested sedimentation was derived from Bukit Barisan in the southwest. Geochemical data also shows that the highest TOC is situated in the main depocenter of the lacustrine shales and coals. Kerogen type of this source rock is type II/III (oil and gas prone) with Ro value on peak oil window. However, the uplift of Bukit Barisan during the Middle Miocene (Eubank & Makki, 1981) has created a challenge with regards to the hydrocarbon play.